Ectomycorrhizal colonization reduces ultra-fine root abundance

Ectomycorrhizal fungi (ECM) form mutualistic associations with tree roots, enhancing nutrient and water uptake and improving tree resistance to drought stress. ECM associations generally improve plant performance but act as strong carbon sinks, altering carbon allocation within the root system and modifying its architecture. A high degree of ECM colonization has been associated with increased root branching and the formation of short, swollen root tips. However, the role of ECM in shaping root system functional architectural traits remains unclear.For instance, root diameter is a key trait differentiating fundamentally different functions, with fine roots mainly serving resource uptake and coarse roots mainly serving axial transport. Yet, studies observed ECM colonization leading to both stimulation and suppression of fine‑root production. These contrasting findings might derive from the widespread use of the